Preparation of nitrolic acids and pseudonitroles



May 28 E; M. NYQGAARD ETAL ,PREPARATION OF NITROLIC ACIDS ANDPSEUDONITROLES Filed Feb. 13, 1945 m 3 5 6 Qbmwm EDWIN M NYG/MRD THOMASr/voz 4N0 INVENTOR5 m @{QM' AGENT Patented May 28, 1946 PREPARATION OFNITROLIC ACIDS AND PSEUDONITROLES Application February 13, 1945, SerialNo. 577,723

14 Claims.

This invention has to do with an improved method for the preparation ofnitrolic acids and pseudonitroles.

It has long been known in the art that nitrolic acids and pseudonitrolesare prepared by reaction a of nitrous acid with primary and secondarynitro- Daraffins, respectively. For example, a nitrolic acid, such aspropyl nitrolic acid, is obtained from primary nitropropane(l-nitropropane), as illus- Similarly, a pseudonitrole, such as propylpseudonitrole, is obtained from secondary nitropropane (Z-nitropropane),as illustrated by Equation II:

HaC

+ IlONO +H20 N02 113C N02 require nitrous acid, per se, or developedinthe preparation from an alkali nitrite and a mineral acid. a

In our copending application, Serial Number 489,066, filed May 29, 1943,with John H. Mc- Cracken, of which the present application is acontinuation-in-part, we have described a novel method for preparingnitrolic acids and pseudonitroles from primary and secondarynitroparaffins, respectively, wherein it is unnecessary to use nitrousacid or its equivalent in the form of an alkali nitrite and mineralacid. This novel method is extremely simple and merely involvescontacting a nitroparaflin with substantially a stoichiometrical amountof an aqueous alkali, thereafter acidifying the nitroparafiin-aqueousalkali mixture at a temperature below about l5- C. with a mineral acidother than nitrous acid, and then separating a nitrolic acid or apseudonitrole from the reaction product so obtained.

We have now discoveredthat the efiiciency of our method outlined above,and described in detail in the aforesaid application, is improvedsubstantially by modifying the same, and it is upon this discovery thatthe present invention is predicated. The method contemplated hereininvolves the feature of adding a mineral acid other than nitrous acid toa nitroparafiln-aqueous alkali mixture or an aqueous mixture of anitroparaflin salt at a rapid rate, with the temperature maintainedbelow about 15 C. and followed by separation of a nitrolic acid or apseudonitrole from the reaction product so obtained. V

The rate of addition of the aforesaid acid to a nitroparafiin-aque'ousalkali mixture or an aqueous mixture of a nitroparaffin salt should berapid in order that maximum yields of nitrolic acids and pseudonitrolesbe realized. We have found that when the acid is added to the saidmixture or salt mixture over an extended period,

as several hours, yields of nitrolic acids and pseudonitroles areappreciably lower and. the amount of nitropa'raffin regenerated in themethod becomes significant. In contrast to this, when the acid was addedall at once or over a very short period, as several minutes or less,high yields of the desired products were obtained. It is preferred, asdemonstrated by the curves in Figure 1, discussed hereinafter, that 0.22mole of mineral acid other than nitrous acid be rapidly added to 0.2mole of said nitroparamn-aqueous alkali mixture or an aqueous mixture ofa nitroparafiin salt during a period of less than 30 minutes, andparticularly preferred are periods of less than 10 minutes.

In the present method other precautions should also be observed in orderto achieve a high degree of efiiciency; although, as aforesaid, therapid rate of addition of mineral acid to a nitroparaffin-aqueous alkalimixture or an aqueous mixture of a nitroparaifin salt is the salientfacto: here. It is desirable, for example, to use a stoichiometricalquantity, or a slight excess, of a relatively strong alkali with thenitroparaflin reactant; however, a large excess of alkali is notconducive to the obtainment of good yields of the desired nitrolic acidsand pseudonitroles. In this connection, when a per cent excess of- 30per cent sodium hydroxide solution was used with 2-nitropropane, theyield of propyl pseudonitrole wa very small. While variousconcentrations of aqueous alkali, as alkali metal hydroxides and alkaline earth metal hydroxides, may be used effectively in the presentmethod, preferred for use are aqueous alkalies having concentrationsfrom about 10 per cent to about 30 per cent. Relatively weak alkalies,such as ammonium hydr x ide and organic amines, are not contemplated theacidification operation.

herein, inasmuch as they are apparently too weakly basic to produce thesalts of the nitroparaflins necessary for reaction with said mineralacid. Accordingly, as used here and in the claims appended hereto, thelanguage relatively strong alkali refers to an alkali metal hydroxide oran alkaline earth metal hydroxide, and thus refers to an alkali suitablefor use in the present method. It will be apparent to those familiarwith the art that the nitroparailln contacted with aqueous alkali isconverted to its corresponding salt and, therefore, it will also beapparent that analysis of our investigations indicates that a reactionmechanism other than the one there proposed most probably obtains.gations point to the following mechanism which is illustrated by thepreparation of propyl nitrolic acid from l-nitropropane,beingrepresented by Equation III below:

an aqueous mixture of a salt of a nitroparaflin' 'also be influenced byheat, although the temperature should not .be brought up to thedecomposition temperature of the mixture or salt.

As indicated hereinabove, temperature plays an important role in ourmethod. Temperatures both high and low, however, may be used when anitroparamn is contacted with an aqueous alkali; yet, temperatures ofthe order of 20-25 C. are preferred for this purpose. Particular careshould be taken in the acidification procedurethat is, during theaddition of a mineral acid other than nitrous acid to thenitroparaflln-aqueous alkali mixture or the aqueous mixture of anitropar'amn sa1t--to maintain the temperature below about 15 C, Ingeneral, temperatures from'about C. to about C. are preferred for It hasbeen found that if the temperature of the reaction mixture so formed isallowed to increase above about 20 C. during acidification, increasingamounts of nitrons oxide (N20) are produced and less nitrolic acid orpseudonitrole is found in the reaction product. In separating thenitrolic acid or pseudonitrole formed in the reaction from the reactionmixture, care must be taken that the temperature is maintained below thedecomposition temperature of the said nitrolic acid or pseudonitrole,lest the yield thereof be lowered considerablyr It will be apparent thatthe decomposition temperature will vary 1 for the individual nitrolicacids and pseudonitroles obtained in the present method; however, it ispreferred that the separation procedure be carried out at temperaturesbelow about 0..

- In the acidification operation, any mineral acid other than :nitrousacid may be used; typical acids are hydrochloric, nitric and sulfuric.The concentration of such mineral acids may be varled considerably, Itis preferred that the mineral-acid have-sucha concentration that no ap-Dreciable-heat is :evolved when the acid is diluted with oraddedtowater. The quantity. of acid used'may be varied over a relativelywide range. but it is desirable to use a slight excelsof acid in theacidification step. llispreviously P inted out irrour'copendingapplication,v identified hteinabove, it is advantageous to keep addedoxygen from the reaction mixture. v

Since filing our above-identified application} 'm The overall reactionIV, on Y H n 2n,o-g-c=0 HQNIOI an on fltrous acid) mmo, mo IIONO Nmon 0H 11 Ill HrC-CC= -OH NsCl (n-pmpyl nitronio acid) N OH H t HsQ-C- N0; HO

(propyl nitrolio acid) The overall reaction from Equation III, (a)through (e), may be represented by Equation III (I)! Following the samereaction. mechanism, a secondary nitroparamn such as 2-nitropropane isOur investithrough (e), may be represented by Equation IV (f):

It is to be understood, however, that the foregoing proposed reactionmechanism is that which appears to obtain on the basis of presentinvestigation; yet, it is not to be construed in any way as a limitationupon the method described herein and defined in the" claims appendedhereto.

To illustrate the effect of rate of addition of a mineral acid-otherthan nitrous acid to a nitroparafiln-aqueous alkali 'mixture or anaqueous mixture of a niroparaflin salt, curves A and B in Figure I 'areprovided. Curve A was obtained with a 2-nitropropane-l0 per cent aqueousNaOH mixture aged for about 10 days at about 25 0.; curve B was obtainedwith a corresponding mixture aged for about 65 days under the sameconditions. In obtaining the said curves, all reaction conditions weremaintained substantially constant while the time of addition was varied.Concentrated HCl (20 cc., equivalent to 0.24 mole HCl) diluted with 6volumes of water and cooled in an ice bath, were added to a solution of0.20 mole of 2-nitropropane dissolved in 0.22 mole of NaOH (10% aqueoussolution), the mixtures :be-

ing constantly agitated. The reaction mixtures so obtained were agitatedfor about 45 minutes after complete addition of the acid. Thetemperatures during addition and during the following period weremaintained below C., the temperature range being from about C. to 0 C.

' The. reaction mixtures so obtained were then allowed to stand forabout 16 hours in a cold room maintained at 1 C. All reaction productswere blue solutions from which a cream colored solid precipitated. Thesolid was filtered onto a Biichner funnel, washed with water, dried onfilter paper and weighed. In each case the solid recently, these,compounds have been foun. to

be extremely efiective ignition improvers in Dieprepared from theircorresponding halogen-subwas the dimeric form of propyl pseudonitrole,

The pure dimer is colorless, melts to a blue liquid and then decomposes.When dissolved in organic liquids, such as benzene, carbon tetrachlorideor acetic acid, adeep blue color is imparted to the organic liquids.This color change is believed to be the result of the dimer changing tothe monomer. The melting point of the solid product is 75 C., and thisis the value reported in the literature for propyl pseudonitrole. CurveA demonstrates the profound eflect of the rate of addition; for example,when the addition'was completed in about 1 minute, the yield was 52 percent; contrasted with this is a typical addition period of about 70minutes whereupon the yield was only 30 per cent. Curve B demonstratesthe same efiect, with complete addition in '7 seconds the yield was 80.1per cent; lesser yields of 68 per cent and 52 per cent were obtainedwith complete addition in about 70 minutes and about 160 minutesrespectively. Curve B, when stituted primary and secondarynitroparafiins',grespectively. In general, any substituent group such ashalogen, keto, amino, hydroxyl, etc. may be present on the nitroparafllnreactant, and thus present on the resulting nitrolic acid orpseudonitrole, so long as the substituent group does not interfere withthe formation of the alkali or alkaline earth metal salt of thenitroparaflln.

Although the present invention has been illustrated hereinabove by thepreparation of specific nitrolic acids and pseudonitroles, it is to beunderstood that these specific embodiments are but representative of ourimproved method for the preparation of compounds of the broad classes ofnitrolic acids and pseudonitroles. Accordingly, the present invention isnot to be construed as limited thereto but is to be broadly construed inthe light of the defining language of the appended claims.

We claim:

1. .The method of preparation of a compound selected from the groupconsisting of a nitrolic acid and a pseudonitrole, which comprises:contacting a mononitroparaffinselected from the group consisting of aprimary and a secondary mononitroparafiin with a relatively strongaqueous alkali; adding a mineral acid other than nitrous acid to themononitroparamn-aqueous alkali reaction product so obtained, at atemperature below about 15 C. at a rapid rate; and separating saidcompound from the reaction mix- I ture obtained in the precedingoperation at a temperature below the decomposition temperature of saidcompound.

2. The method of preparation of a compound selected from the groupconsisting of a nitrolic acid and a pseudonitrole, which comprises:contacting a mononitroparafiln selected from the group consisting of aprimary and a secondary mononitroparaiffin with substantially astoichiometrical amount of an aqueous alkali selected from the groupconsisting of an aqueous alkali metal hydroxide and an aqueous alkalineearth metal hydroxide; adding a mineral acid other than nitrous acid tothe mononitroparafiin-aqueous alkali reaction product so obtained, at atemperature below about 15 C. at a rapid rate; and separating saidcompound from the reaction mixture obtained in the preceding operationat a temperature below the decomposition temperature of said compound.

3. The method of preparation of a compound selected from the groupconsisting of a nitrolic acid and a pseudonitrole, which comp-rises:contacting a mononitroparaflin selected from the group consisting of aprimary and a secondary mononitroparaflin with substantially astoichiometrical amount of an aqueous alkali metal hydroxide; adding amineral acid other than nitrous acid to the mononitroparaffin-aqueousalkali reaction product so obtained, at a temperature below about 15 C,at a rapid rate; and separating said compound from the reaction mixtureobtained in the preceding operation at a temperature below thedecomposition temperature of said compound.

4. The method of preparation of a compound selected from the groupconsisting of a nitrolic acid and a pseudonitrole, which comprises:contacting a mononitroparafiin selected from the group consisting of aprimary and a secondary mononitroparaflin with a relatively strongaqueous alkali; aging the mononit'roparamn-aqueous alkali reactionproduct so obtained; adding a mineral acid other than nitrous acid tothe said aged mononitroparaflin-alkali reaction product, at'atemperature vbelow about C. at a rapid rate; and separating saidcompound from the reaction mixture obtained in the preceding operationat a temperature below the decomposition temperature of saidcompound. vJ

5. The method of preparation of a compound selected from the groupconsisting of a nitrolic acid and a pseudonitrole, which comprises:adding a mineral acid other than nitrous acid at a rapid rate at atemperature below about 15 C. to an aqueous solution of a salt 01' amononitroparaiiin selected from the group consisting of a primarymononitroparamn and a secondary mononitroparaflin, said-salt beingselected from the group consisting of an alkali metal salt and analkaline earth metal salt; .and separating said compound from thereaction mixture obtained in the preceding operation at a temperaturebelow the decomposition temperature of said com-" 7 pound.

' 8'.-'I'he method of preparation of a compoundv selected from the groupconsisting of a nitrolic acid and a pseudonitrole, which comprises:adding a mineral acid other than nitrous acid at a rapid rate at atemperature below about 15 C. to an aqueous solution of an alkali metalsalt of a mononitroparaflin selected from the group consisting of aprimary mononitroparaflin and a secondary mononitroparaflin; andseparating said compound from the reaction mixture obtained in thepreceding operation at a temperature below the decomposition temperatureof said compound.

7. Thevmethod' of preparation of a compound selected from the groupconsisting of a nitrolic acid and a pseudonitrole, which comprises:adding a mineral acid other than nitrous. acid at a rapid rate at atemperature, below about 15 C. to an aged aqueous solution or a salt ofa mononitroparaflin selected from the gro'upconsisting of a primarymononitroparaflin and a secondary mononitroparamn, aid saltbeingselected from the group consisting of an alkali metal salt and analkaline earth metal salt; and opertaing said rapid .rate at atemperature below about 15 C; to an aged aqueous solution of. an alkalimetal salt 01' a mononitroparaflin selected from the group consisting oia primary mononitroparamn and a secondary mononitroparaflin; andseparating said compound from the reaction mixture obtained in thepreceding operation at a tempera-' ture below the decompositiontemperature oi said compound. v I

amount of aqueous sodium hydroxide; adding a I mineral acid other thannitrous acid to the 2- nitropropane-aqueous sodium hydroxide reaction 4product so obtained, at a temperature below about 15 C. ata rapid rate;and separating said propyl pseudonitrole from the reaction mixtureobtained in the preceding operation low about 15 C.

10. The method or preparation of propyl pseudonitrole, which comprises:contacting 2-nitropropane with substantially a stoiehiometrical amountof aqueous sodium hydroxide; adding a at a temperature bemineral acidother than nitrous acid to the 2- donitrole, which comprises:contacting2-nitropropane with substantially a stoichiometrical amount ofaqueous sodium hydroxide; ag g e z-nitropropane-aqueous sodium hydroxidereaction product so obtained; adding a mineral acid other than nitrousacid to the aged z-nitmpmpane-aqueous sodium hydroxide reaction product,at a temperature below about 15 0. ate rapid rate; and separating saidpropyl pseudonitrole from the reaction mixture obtained in the precedingoperation at a temperature below about 15 C.

12. The method of preparation 0! propyl pseudonitrole, which comprises:adding a mineral acid other than nitrous acid at a rapid rate at atemperature'below about 15 C. to an aqueous solution of a salt of2-nitropropane, said salt being selected from the group consisting of analkali metal salt and an alkaline earth metal salt; and separating saidpropyl pseudonitrole tromvthe reaction mixture obtained in the precedingoperation at a temperature below the decomposition temperature oisaidpropyl pseudonitrole,

13. The method of preparation 0! propylpseu donitrole, which comprises:adding amineral acid other than nitrous acid at a rapid rate at atemperature below about 15 C. to an aged aqueous trolic acid,whichcomprises: contacting 1-nitropropane with substantially astoichiometrical' amount- 01 aqueous sodium hydroxide; adding a mineralacid other than nitrous acid to the l-f nitropropane-aqueous sodiumhydroxide reaction product so obtained, at a temperature below about 15C. at a rapid rate; and separating said propylnitrolic acid from thereaction mixture. obtained in the preceding operation at a temperaturebelow about 15 C,

EDWIN M. N'YGAARD. THOMAS Noll-AND.

